jcaises



April 26, 1927.

G. SEIBT METHOD OF MAKING THIN METAL SHAPES Filed Sept- 26, 192 4 Patented Apr. 26, 1927.

UNlTED STATES GEORG SEIB'I, OF BERLIN-SCHONEBERG, GERMANY.

METHOD OF MAKING THIN-METAL SHAPES.

Original application filed July 23, 1923, Serial No. 653,396.

Divided and this application filed September 26, 1924, Serial No. 740,108, and in Germany January 9, 1923.

My invention relates to the method of working thin metal sheet into extremely thin forms, so as to be of uniform thickness, and tlllci application is a division of my application berial l\o. 6523,2396, filed July 23, 1923.

The object of my invention is to draw or to extend a liat sheet of aluminum, copper, nickel or other metal into a suitable shape that is extremely thin or foildike, the thickness being but a few hundredths of a millimeter, specifically less than live hundredths of a millimeter.

The articles that I have so produced are extremely delicate diaphragms for sound reproducing apparatus whose form is not fiat, and generally of a curved cross-section, as of a sphere or similar regular curved body.

The iinished product is so thin and foillike that it cannot be pressed between metal dies, as the dies will tear the metal when the patrix is removed.

i am enabled to produce such thin diaphragms by supporting a thin sheet metal at its edges and distendiug or drawing the metal by means of a plastic patrix, preferably air under high pressure.

My method will be explained in connection with the apparatus shown in the accompanying drawings, in which Figure l is a cross-section of one form of device for carrying out my method, and

Fig. 2 is a cross section of another form.

'lhin diaphragms for talking apparatus which are made in the form of cups with straight walls (hollow cones) or cups with curved walls for the purpose of stiffening the diaphragmsg are already known in the art. eta: those known diaphragms are of considerable thickne so that they do not meet certain requirements. Some of these diaphragms are also not designed so that all parts of the same vibrate in phase with each other. others do not have a sufliciently high natural rate of vibration, and a drawback of others is that the annular ring joining the periphery of the diaphragm with the pe ripheral clamping device does not consist of a single piece of non-perforated sheet metal.

If, as has already l'ieen proposed, the periphery of the cup-shaped diaphragm is only joined to its peripheral clamping device or support by narrow radial strips between sector-shaped or arcuate perforations, :1 diaphragm which is as thin as that made in accordance with this invention, would be deformed to an unpermissible extent by the operation of stamping out the perforations. And if, as has already been proposed, the still cup-shaped diaphragm be fixed to a separate, thin, elastic clamping ring of prepared paper, fabric, or the like, a diaphragm of the requisite thinness would also be deformed during manufacture when the apparatus is assembled.

Moreover, a diaphragm thus consisting of two parts (the diaphragm proper and the annular clamping ring) would be liable not to vibrate in unison at all parts of its surface, i. e., different elements of its surface would be liable to vibrate out of phase with each other.

in accordance with this invention the rim of the cup-shaped part of the diaphragm joins immediately onto a fiat, annular, nonperforated ring which is adapted to be clamped or held in the peripheral clamping or supporting device.

Diaphragms which are thin, light and still enough, and are sufliciently free of internal stresses for the purposes of the present invention cannot be produced by processes of the kind proposed hitherto for similar purposes. Attempts have been made to produce cup-shaped, spherical, or curved metal diaphragms by depositing metal upon a surface of wax of the desired shape after making the said surface capable of conducting electricity.

Useful results might possibly be obtained, with difficulty, by this method when empl0ying copper or nickel, but when aluminum is employed, which, as is well known, cannot be deposited electrolytically in thin layers, this method is useless. Moreover, the separation of the thin layer or metal skin from the wax surface is fraught with great difficulties, and is thus liable to destroy the skin.

Attempts have also been made to produce conical, thin aluminum diaphragms by spinning, i. e., by applying pressure by means of a burnisher or the like to the sheet metal while it is rotated in a lathe. This spinning process is applicable with metal of a thickness down to about 0.05 mm. and diameters of about 50 mm. A disc of the sheet alumi n um is fixed at its periphery in a chuck rotated by the lathe. During rotation pressure is applied by a blunt tool until the desired shape is produced. This process becomes impracticable when greater diameters or thinner sheet metal are, or is, employed.

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Besides, it will not answer for diaphragms of considerable cavitation. lts greatest drawback is that it gives rise to internal stresses in the diaphragm which result in rattling noises when the diaphragms are used for the reproduction or the voice. These noises are quite insupportahle when the talking apparatus-z is energized with considerable power, as in the case of loud speaking telephones or the like.

In accordance with my invention all these disadvantages are avoided by shaping the diaphragm with the aid of a drawing; process in "which the patrix expands the thin sheet metal quite unit'ormly.

l have found it preferable to use a patrix which has no precisely defined shape, but which consists of a plastic material such as a fluid, as compressed air, thicl: grease, oil, or water under pressure. It a diaphragm is to be produced for a talking; apparatus in which hollow spherical shape required, the drawing device shown in Fl 1 will su'l? lice. The diaphragm in the form of a that disc is clamped at its periphery and compressed air is introduced into the device from above, so as to cause the diaphragm to bulge downwardly as indicated in Figure 1.

To produce a diaphrz 11 ot the shape re quired for another tall-.ing apparatus, and having a flat central bottom! or other irregular shape, a matrix as shown in Figure 2 is employed, which detines the shape oi the diaphragm when the compressed air is introduced from above. [in air p ressure of up to about live atmospheres per sq. cm. is applied and this causes the diaphra nu to be pressed lirn'ily against the cavitated surface of the matrix.

To obtain a deep cavitation the drawing process is preferably carried out in several steps. l n a single step an aluminum diaphragm oi 100 mm. in diameter and a thiclc ness of 0.03 mm. can only be bulged to a depth of about let nuns. ii cayity of a depth of 19 nuns. can be obtained, however, it the drawing process is carried out in three steps and the metal is annealed by heating it at each step to about 300 to 350 C. It is important to use temperatures between these limits because a ten'iperature of say only 220 is practically useless with alul'ninum, and temperatures above 400 are actually in jurious because they result in. tearing of the metal.

By tollowin the aforesaid instructions aluminum diaphragms as thin as 0.02 mm,

of a diameter of '70 nuns. and a cavity 14 nuns. deep may be produced;

lit has already been proposed to shape diaphragms tor talking apparatus by means of compressed air, but in these proposals it was not a question of making diaphragms of light metal and extreme thinness and great stiii ness by drawing, but of producing celluloid diaphragms of unusual elasticity but not conical nor cup-shaped, and at the same time oi a thickness of only a few tenths ol? a millimeter. Diaph 'agnr-s of this kind are not within the scope of this invention because the y do not enable the desired technical elij'ect to be obtained but result in a contrary el'lect.

1. A. method of making extremely thin toil-like sound reproducing dia'phrz'igms which coniprises cla-n'ipEng; a thin sheet of aluminum around its edges and producing a drawi pressure on one surface of the ii'letal by means of a plastic mediuu'i until the metal. is reduced to a lilllCl ZllPSS less than .05 of a n'iillimeter.

2. The method of making extremely foil-like hollow thin sound reproducing diaplu'a'gms which comprises clamping a thin sheet oi aluminun'i arouiid it? edges and producing a drawing pressure by fluid. on one suriiace ot' the n'ietal sheet to partially entend the metal, annealing the partly termed. sheet by heating the same to amaroximately 300 to 350 (l. and then continuing the e);- tension oi the metal to obtain a thiclmess less than .05 of a millimeter.

8. The method of making extremely thin foil-like sound reproducing diaphragnis which comprises clampi a thin sheet oi circular metal of appr miniately T0 millimeters in diai'i'ieter aroluid its edges and producing; a drawing pr ure on one surface of the metal by means of a 1')lastic medium until the metal is reduced to a thickness less than 0.5 of a millimeter and having; a cavity of approximately l t llllllllllQlClS in depth.

In testimony that I claim the foregoing: as my invention, 1 have signed my name hereto.

lEOllG- SEIBT. 

